The present invention relates to microwave radiometry technology and, in particular, to an apparatus for non-invasively measuring temperature distribution within a human body including the human skull for brain intracranial diagnostic applications.
Many researchers have proposed and used, to some extent, microwave radiometry technology to non-invasively measure temperature distribution within the human body during the past 30 years. The reason for this is the fact that microwaves in the frequency range of 1-5 GHz penetrate through human tissues sufficiently and also provide sufficient directivity to measure the temperature distribution within the body. One reason for proposing to use microwave radiometry technology is the failure of infrared (IR) thermography techniques to provide useful information for temperature distribution within a human body including the human skull for brain intracranial diagnostic applications. This is due to the fact that although the human body emits maximum radiation at infrared (IR) wavelengths, the very high attenuation of this radiation passing through tissues make the IR thermography techniques of only limited value.
A publication entitled xe2x80x9cMicrowave Thermography: Principles, Methods and Clinical Applicationsxe2x80x9d by P. C. Myerst et al in the Journal of Microwave Power 14(2), 1979 (pages 105 to 115) describes one type of microwave thermography technology where an antenna in the form of 1xc3x972 cm rectangular waveguide filled with a low-loss solid is placed flush against the skin. The human body, as P. C. Myerst et al indicated, emits thermal radiation with an intensity that is proportional to tissue temperature and that at microwave frequencies of 3 GHz, the intensity is reduced by a factor of xe2x89xa1108 from the maximum intensity at an IR wavelength of xcex=10 xcexcm. A microwave radiometer, however, can detect radiation with that intensity and determine changes in temperature of less than 1xc2x0 C. in the human body. Since microwave radiation can penetrate human tissue for distances of several centimetres, this allows for the detection of variations in subsurface temperature. P. C. Myerst et al reported building three different radiometers to use with the rectangular antenna which operated at 1.3, 3.3 and 6.0 GHz. Tests were performed on patients at 1.3 and 3.3 GHz with results being reported in the publication.
Another publication by J. Edrich on pages 95 to 104 of the same journal entitled xe2x80x9cCentimeter- and Millimeter-Wave Thermographyxe2x80x94A Survey on Tumour Detectionxe2x80x9d describes further thermography instrumentation which operate at centimeter (cm) and millimeter (mm) wavelengths that can directly measure subcutaneous temperature in a human body. In this publication, the radiometry involved remote sensing by focussed apertures like lenses or reflectors that focus the cm or mm wave into a horn antenna mounted on a scanner. The scanner can be moved in a raster fashion over a patient lying on a bed. J. Edrich indicates that this type of scanner is better suited for high frequencies because of the requirement for an aperture diameter of many wavelengths but that going to higher frequencies will decrease penetration. However, more power is received at higher frequencies because the beam becomes narrower. J. Edrich states on page 98 that xe2x80x9cAs compared to the contacting method at 3 GHz, remote sensing at 9 GHz therefore results in an incremental antenna temperature that is twice as large and a subcutaneous resolution area of less than one eightxe2x80x9d. J. Edrich then further states that xe2x80x9cCentimeterwave radiometry at this frequency should therefore be well suited for remote and reproducible probing of subcutaneous temperatures.xe2x80x9d
Another publication by Kenneth Carr et al in the IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-29, No. 3, March 1981 entitled xe2x80x9cDual-Mode Microwave System to Enhance Early Detection of Cancerxe2x80x9d on pages 256 to 260 describes an active microwave transmitter to provide localized heating taking advantage of differential heating of a tumour with respect to surrounding tissue and a passive microwave radiometer to permit early detection of a cancer. In this system, the microwave radiometer frequency was chosen to be at 4.7 GHz whereas the microwave heating frequency was at 1.6 GHz.
The temperature distribution inside the human body including the human skull for brain intracranial diagnostic applications can be measured up to at least 5-7 cm depths with microwave radiometry. However, there is a practical problem in sensing the radiated intercranial thermal energy at microwave frequencies since this would require an array of microwave antennas to coherently integrate the scattered thermal energy and localize the source area inside the human brain.
It is an object of the present invention to provide a microwave radiometry apparatus that is able to non-invasively and more accurately measure the temperature distribution within dielectric bodies such as in a human body including the human skull for brain intracranial diagnostic applications.
A microwave thermography apparatus, according to one embodiment of the invention, for measuring a temperature distribution within a dielectric body, comprises an ellipsoidal cavity having an electrical conductive surface wherein said body can be located at one focus of said cavity, a microwave antenna being located at a second focus of said cavity, which antenna is connected to a radiometer that amplifies and filters signals detected by the antenna before those signals from the radiometer are applied to a detector connected to an output of the radiometer.